Method and system for the production of a seamless hot-rolled tube as well as a rolled centrifugally cast tube and use of a hollow block produced by means of centrifugal casting

ABSTRACT

Sensitive hollow blocks or tubes are elongated in a hot-forming elongator while maintaining, if possible, the internal structure that is present or that forms immediately after casting, and thereby, in the case of suitable method management, even thin-walled tubes or tubes rolled from centrifugally cast hollow blocks can be made available to a sufficiently operationally reliable extent. As a result, for the first time, it is possible for rolled centrifugally cast composite material tubes to be made available and for composite material hollow. blocks produced using centrifugal casting to be utilized for the production of a seamless tube.

CROSS REFERENCE TO RELATED APPLICATIONS

Applicant claims priority under 35 U.S.C. §119 of German Application No. 10 2016 106 025.9 filed Apr. 1, 2016, the disclosure of which is incorporated by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The invention relates to a method for the production of a seamless hot-rolled tube as well as to a system for the production of a seamless hot-rolled tube, comprising a hollow-block casting unit and an elongator that follows the hollow-block casting unit. Furthermore, the invention relates to a rolled centrifugally cast tube and to the use of a hollow block produced by means of centrifugal casting.

2. Description of the Related Art

Methods and systems for the production of seamless tubes are presented in an overview in DD 68 215, for example. In these methods and systems, first of all, hollow blocks are obtained using the extrusion method, and subsequently, they are passed to elongators, such as a pilger rolling mill, a plug rolling mill, a push bench or a continuous rolling mill, by way of a three-roll cross-roll piercing mill as well as other cross-roll piercing mills, and subsequently or also post-treated by a reeler, and then passed to a calibration unit, such as a becking mill, a sizing mill or an elongation reduction system, by way of a reheating furnace. In this regard, the workpiece to be treated, in each instance, can be hot-rolled or cold-rolled.

From the GB 1 298 323 or from the DE 19 06 961 A having the identical priority, it is known to obtain hollow blocks with an extrusion method, and prestretch those blocks in a hot pilger rolling mill, before they are finally rolled in an elongator, namely in a continuous rolling mill.

Also, for example, the publication by V. M. PARSHIN et al., Production of hollow Continuous-Cast Billet for Seamless Pipe, ISSN 0967-0912, Steel in Translation, 2012, Vol. 42, No. 12, pp 825-829© Allerton Press, Inc., 2012, describes that seamless tubes can be produced using hollow blocks that are obtained by centrifugal casting or extrusion, in that these blocks, after removal of scale, are elongated and then rolled again. Here, as well, they first pass through cross-roll piercing mills, which are referred to as Piercing mill there.

In this connection, it has been shown that particularly sensitive hollow blocks or tubes, such as, for example, comparatively thin-walled tubes or hollow blocks produced using centrifugal casting, cannot undergo these processes, because a great number of surface defects, for example, occurs in the ultimate rolled tube, as PARSHIN et al. already determined, for example. This inability is true especially for rolled centrifugally cast composite material tubes that could not be produced reliably, although the DE 502 155 C or the DE 16 02 116 C suggest the production of well-known centrifugally cast tubes by pilger rolling.

SUMMARY OF THE INVENTION

It is the task of the present invention to make available a method and an apparatus for production of a seamless hot-rolled tube, which handles the workpieces gently, as well as corresponding tubes and the use of corresponding hollow blocks.

These and other tasks are accomplished by systems and methods for the production of seamless hot-rolled tube as well as of rolled centrifugally cast tubes, and by the use of hollow blocks produced by means of centrifugal casting, having the characteristics of the invention. Further advantageous embodiments, if applicable also independent of these characteristics, are found below.

In this regard, the invention proceeds from the fundamental recognition that sensitive hollow blocks or tubes should be elongated in a hot-forming elongator while maintaining, if possible, the internal structure that is present or that forms immediately after casting, and thereby, in the case of suitable method management, even thin-walled tubes or tubes rolled from centrifugally cast hollow blocks can be made available to a sufficiently operationally reliable extent. This accordingly also makes it possible, for the first time, for rolled centrifugally cast composite material tubes to be made available and for hollow blocks produced by means of centrifugal casting to be utilized for the production of a seamless centrifugally cast composite material tube.

Thus, it was possible to determine that a method for the production of a seamless hot-rolled tube, which is characterized in that a cast hollow block is elongated in a hot-forming elongator, with the circumvention of a cross-roll piercing step and with an elongation of 10 or less, handles the respective workpieces gently, with the method management also remaining suitable otherwise.

Obviously, cross-roll piercing appears to intervene in the material structure of a cast hollow block in such an intensive manner that a corresponding quality of the workpiece made available in this manner can no longer be guaranteed. Actual elongation then takes place in hot-forming manner, in the elongator. This drawback is true, also, for a pilger rolling process as it is explained in the GB 1 298 323, for example, which pilger rolling process is upstream of an elongator, itself, and which pilger rolling process has to act upon the workpiece with elongation above 11, in order to prestretch the workpiece for the elongator itself sufficiently.

Multiple experiments have shown that it is not compulsory to eliminate a cross-roll piercing step, as long as the interventions in the material structure that occur during cross-roll piercing are not overly severe. In this regard, a method for the production of a seamless hot-rolled tube that is characterized in that a cast hollow block is elongated in a cross-roll piercing mill, at an elongation below 1.5, in a hot-forming elongator with an elongation of 10 or less, also handles the respective workpieces gently.

Such an interposition of a cross-roll piercing step appears to be particularly practical if eccentricities above 4% can be found in the cast hollow block, which eccentricities can be correspondingly reduced by means of the cross-roll piercing step. If necessary, such an interposition can also take place at eccentricities above 3.8%, particularly above 3.6%.

In the present connection, the term “elongation” refers to the ratio of incoming cross-sectional area to outgoing cross-sectional area of the respective workpiece as it passes through the corresponding rolling mill or during the corresponding rolling method step.

A method for the production of a seamless hot-rolled tube, which is characterized in that a cast hollow block is elongated using at least a part of the casting heat, in a hot-forming elongator with an elongation of 10 or less, already handles the respective workpieces in sufficiently gentle manner. This feature appears to result because if at least part of the casting heat is utilized, the time that elapses between the casting process for production of the cast hollow block and the hot-forming elongator cannot be selected to be too great, so that corresponding crystallization processes in the workpieces or also complicated forming processes in these workpieces are allowed. Elongation in the hot-forming elongator, on the other hand, appears to act on the respective workpieces in gentle manner or to the correct extent.

A system for the production of a seamless hot-rolled tube includes a hollow-block casting unit, an elongator disposed after the hollow-block casting unit, and a conveying segment between the hollow-block casting unit and the elongator that is sufficiently short so that part of the casting heat is utilized for elongation in the elongator, wherein said conveying segment between the hollow-block casting unit and said elongator is interrupted by a furnace. This system is also correspondingly gentle on the workpieces. In this regard, it is understood that corresponding advantages can be destroyed by harmful method actions, such as, for example, an artificial cooling process, without the systems losing their suitability for acting on workpieces in correspondingly gentle manner.

In this regard, it is understood that the respective conveying segment can also comprise required intermediate steps, such as possible separation processes or even the interposition of a cross-roll piecing mill as already explained above, if elongation is sufficiently low.

With regard to elongation in a possible cross-roll piercing mill, it should furthermore be emphasized that at low elongation, particularly at elongation below 1.4 or even below 1.3, even more gentle handling of the workpieces can be achieved.

After elongation in the elongator, the hollow block or the workpiece produced from the hollow block by elongation is preferably calibrated in a calibration unit. In this way, the dimensional accuracy of the tubes produced in this manner, in particular, can be ensured. Accordingly, it is advantageous if the elongator is followed by a calibration unit in the production system.

In particular, a sizing mill and/or an elongation reduction rolling mill can be used as a calibration unit; these mills are sufficiently known from the state of the art.

In general, calibration will take place without an inner tool in the calibration unit, as is already sufficiently known from the state of the art.

Consequently, it is of an advantage if the workpiece runs only once through an elongator, and especially not through a further elongator. It would be very complex keeping the casting heat within the workpiece until this workpiece would have passed the second elongator, too.

As was already explained above, the aforementioned methods and systems handle the workpieces worked on, in each instance, in gentle manner. They are particularly suitable for the production of seamless hot-rolled metallic tubes, particularly if these tubes have a diameter below 17.78 cm (7″) and/or a wall thickness clearly below 100 mm. In particular, the aforementioned methods and systems are suitable for rolling a composite material hollow block produced by means of centrifugal casting, wherein in this way, a seamless hot-rolled tube in the form of a hot-rolled centrifugally cast composite material tube is made available.

Contrary to the opinion known from the state of the art, it is therefore possible, for the first time to make available composite material hollow blocks produced by means of hollow casting for the production of seamless tubes, on the one hand, and rolled centrifugally cast composite material tubes, on the other hand. Accordingly, a rolled centrifugally cast tube that is characterized in that the rolled centrifugally cast tube is a hot-rolled centrifugally cast composite material tube, as well as the use of a composite material hollow block produced by means of centrifugal casting for the production of a seamless hot-rolled tube, which is then accordingly produced to form a hot-rolled centrifugally cast composite material tube, is advantageous.

It has been shown namely that the systems and methods explained above are particularly suitable for rolling of multilayer tubes, particularly for rolling of multilayer metal tubes. This suitability particularly holds true also for multilayer tubes or composite tubes for which a related composite material hollow block was made available using the centrifugal casting method. It is true that the production of composite tubes by means of centrifugal casting is known. It is also possible, however, for the first time to roll them, and to so roll them immediately after casting, in particular, without further complicated measures having to be used between the rolling process and casting.

Accordingly, it is advantageous if a composite material hollow block, produced by means of centrifugal casting, is used for the production of a seamless hot-rolled centrifugally cast composite material tube. Also, it is also advantageous, accordingly, if the rolled centrifugally cast tube is a rolled or hot-rolled centrifugally cast composite material tube, accordingly. The corresponding centrifugally cast tube can then also be referred to as having bimetallic properties.

If necessary, the hollow block can be heated in the elongator before elongation. This feature is particularly advantageous if—for whatever reason—it does not apply that elongation in the hot-forming elongator takes place using at least part of the casting heat. This elongation, however and especially, can also take place to support the hot-forming elongation process.

On the other hand, it is understood that to utilize at least part of the casting heat, something that of course also serves to save energy, the conveying segment between the hollow-block casting unit and the elongator is interrupted at most by a furnace and/or by a severing unit. In this manner, it can be ensured that only absolutely necessary measures, which can lead to a time delay between the casting process and the hot-forming elongation process, are undertaken. Of course, the shortest possible conveying segment, i.e. one that the workpiece passes through quickly, serves for this purpose.

A severing unit can be necessary between the hollow-block casting unit and the elongator if the cast hollow block is so long that it cannot be stretched to one length in the elongator. If the severing unit is designed appropriately, in that it works extremely rapidly and possibly actually runs along with the cast hollow block, a time loss can be reduced to a minimum. It is also conceivable to operate two or more elongators next to one another, in order to avoid possible time losses that could be caused by pieces of the divided hollow block having to wait until they are elongated.

Preferably, the conveying segment between the hollow-block casting unit and the elongator runs without interruptions and has a lock system to and from the furnace, wherein in this connection, a required severing unit is not viewed as being an interruption, as long as the delay caused by it is sufficiently short. This feature makes it possible to feed the cast hollow block to the elongator as quickly as possible. Possible workpieces, such as severed parts of a hollow block, can then be moved out of the conveying segment by way of the lock system and temporarily stored in a furnace. At the proper time, they can then be moved out of the furnace and back into the conveying segment, where they can then reach the hot-forming elongator directly. This system structure permits the greatest possible utilization of at least part of the casting heat, if the corresponding method procedures are suitably coordinated with one another.

Besides hollow blocks being passed to the elongator with the arrangement mentioned above, the conveying segment of the arrangement mentioned above is consequently interrupted by the furnace. Accordingly, although it is thinkable that every hollow block is passing through the furnace, some of them might pass the furnace very fast, if necessary. Under the latter circumstances, the conveying segment to the elongator passing the furnace may be omitted.

Preferably, the furnace accordingly acts as a buffer. It can also be utilized for reheating, if necessary, if the casting heat present in the respective hollow block is not sufficient to ensure a hot-forming elongation process. Also, the furnace can serve for temperature equalization, if necessary, if process-related problems in this regard were to occur. This possibility is directed especially to a stabilization of the temperature if the hollow blocks come out of the hollow-block casting unit with somehow varying temperatures. This situation might result because the parts of the hollow block being casted first have a longer period to cool down than the parts of the hollow block being casted last. Additionally, it might be helpful, accordingly, to temper separate parts of the hollow block after the hollow block has been separated into parts by a severing unit, within a furnace used as a buffer, until the single hollow block parts can be processed further, because, under certain circumstances, this time period might be different for the single hollow block parts.

Accordingly, it is advantageous if the hollow block is tempered in a furnace being used as a buffer before elongation. Especially, this tempering might happen if casting heat still is within the hollow block so that it will not cool down ahead of the elongator, and so that the crystallization processes will correspond to the state after the casting.

It is understood that the furnace can also be utilized, in general, for heating of a stored cast hollow block, if at least part of the casting heat was not utilized, for whatever reason.

Any suitable casting unit for the production of hollow blocks can be used as a hollow-block casting unit. In particular, for ergonomic reasons, hollow-extrusion units, some of which can actually be configured to work continuously, are possible. In such cases, a saw or other severing unit must be provided. In particular, a centrifugal casting unit can also be used as a hollow-block casting unit, wherein here, both discontinuous and continuous centrifugal casting units, whether they are oriented vertically or horizontally or in mixed form, can be used. In the case of continuous casting units, it is accordingly advantageous if a severing unit follows them. Obviously, a severing unit might be used in combination with other casting units.

With regard to method management, it is understood, accordingly, that the cast hollow block can be cast particularly by means of extrusion or centrifugal casting, in the orientations mentioned above, and also continuously or discontinuously. It is understood that if necessary, other casting methods can also be used to corresponding advantage.

Primarily, any unit with which an elongating elongation process can be exerted on a cast hollow block is suitable as an elongator. In particular, pilger rolling mills or longitudinal rolling mills such as a push bench, plug rolling mills or continuous rolling mills can serve for this purpose. In general, the elongator will work with an inner tool in order to be able to produce sufficient dimensional accuracy and a suitable elongation reduction process.

Accordingly, the elongator of the presented arrangement is the rolling unit in which the inner diameter of each rolled tube is determined, or in which the inner surface of each rolled tube is finally subjected to rolling forces by an inner working tool.

Particularly preferably, a longitudinal rolling mill is used as an elongator, because here, a particularly gentle rolling process takes place. In this connection, it should be emphasized that a pilger rolling mill as such cannot be referred to as a longitudinal rolling mill, because the pilger process should actually be classified as a forging process.

The use of a push bench as a longitudinal rolling mill has proven to be particularly preferable and advantageous with regard to its action on the respective hollow blocks. This quality particularly holds true if the push bench has rolls that act in forming manner, particularly a plurality of rolls that act in forming manner, which are disposed on multiple frames, and if fixed lock rings or the like are preferably eliminated.

Preferably, the elongator or, in particular, the longitudinal rolling mill and especially the push bench cause elongation of 2 or more. In this manner, the elongator can take on the deformations that are undertaken, as such, by the cross-roll piercing step or by a cross-roll piercing step that has a relatively strong effect, in part or, if possible, as a whole. In particular, it is then unnecessary for interventions to be required for correction, accordingly, in subsequent processing steps, such as in the calibration unit, for example.

In order to act gently on the hollow block being elongated, in each instance, it is advantageous if the elongator or, in particular, the cross-roll piercing mill and especially the push bench have an elongation of 10 or less.

It is understood that the characteristics of the solutions described above and in the claims can also be combined, if applicable, in order to be able to implement their advantages cumulatively, accordingly.

Advantageously, the elangator is elongating the hollow block with an elongation of 8 or less which is accordingly gentle to the working piece, especially if this working piece is a composite material. In particular, it is accordingly of advantage if the cast hollow block is elongated in the hot-forming elongator with an elongation of 7 or less.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features, advantages, goals, and properties of the invention will become apparent from the following detailed description considered in connection with the accompanying drawings and exemplary embodiments. It is to be understood, however, that the drawings are designed as an illustration only and not as a definition of the limits of the invention.

In the drawings,

FIG. 1 shows different variants with regard to production systems and methods for the production of a seamless hot-rolled tube; and

FIG. 2 is a schematic cross-section through a centrifugally cast composite material tube.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The production system for the production of seamless hot-rolled tubes shown schematically in FIG. 1 first of all comprises a hollow-block casting unit 10, which is followed by an elongator 20 over a conveying segment 41, 42. The elongator 20 is followed by a calibration unit 30 over a conveying segment 43, so that a hot-rolled tube can be made available from a cast block, by way of the elongator 20 and the calibration unit 30.

In this regard, the conveying segment 41, 42 is configured to be so short that the casting heat can be utilized during elongation, as well. As is evident, there is no cross-roll piercing mill between the hollow-block casting unit 10 and the elongator 20, wherein—if necessary—a cross-roll piercing mill having a slight elongation, for example of 1.2 to 1.4, can be provided here.

A furnace 50 is provided in the conveying segment 41, 42 between the hollow-block casting unit 10 and the elongator 20. Preferably, the furnace 50 is situated not directly in the conveying segment 41, 42, but rather a lock system is provided, through which the cast hollow blocks can be moved out of the conveying segment 41, 42 and back into it again. Accordingly, working pieces might reach the elongator 20 directly, bypassing the furnace 50, which is enabling a direct use of the casting heat and, by the way, which is positive with respect to the use of energy. The working pieces might be tempered or kept at temperature within the furnace 50. In alternative embodiments, a lock system might be omitted so that every hollow block is passing through the furnace 50 with some working pieces having appropriate temperatures, passing through the furnace 50 to the elongator 20 very fast, if necessary.

In particular, rotary hearth furnaces 51, reverbatory furnaces 52 or induction furnaces 53 can be used as a furnace 50.

If considered necessary, a reheating furnace 54 can be provided in the conveying segment 43 between the elongator 20 and the calibration unit 30.

Likewise, it is possible that a severing unit (not shown) is also provided in the conveying segment 43.

In particular, a horizontal discontinuous centrifugal casting unit 11 or a vertical continuous centrifugal casting unit 12 is possible as a hollow-block casting unit 10. In general, the discontinuous centrifugal casting unit 11, just like other discontinuous casting units, will not require a severing unit for severing the cast hollow blocks if the subsequent system stages are appropriately coordinated with the casting unit.

In the vertical continuous centrifugal casting unit 12, as shown schematically in the sketch, a saw is provided, wherein the cut-off pieces are then removed and transferred to the conveying segment 41. It is also conceivable that the continuous centrifugal casting unit is tilted to allow discharge of the hollow blocks. Here, too, a severing unit can be provided, if necessary.

Furthermore, horizontally terminating hollow-extrusion units 13 or vertical hollow-extrusion units 14 can also be used as a hollow-block casting unit 10; in general, they are followed by a severing unit 60 after a conveying segment 44. In the present exemplary embodiment, this unit is provided as a saw 61, wherein here, of course, other severing units, with which hollow blocks can be severed with sufficient speed, can be provided.

It is understood that if necessary, horizontal continuous centrifugal casting units can be used as a hollow-block casting unit 10, behind which units a severing unit 60 can be provided after a conveying segment 44.

In particular, longitudinal rolling mills 21 are used as an elongator 20, for example a push bench 22, a plug rolling mill 24 or a continuous rolling mill 25. Likewise, a hot pilger rolling mill 23 can be used as an elongator 20.

In particular, sizing rolling mills 33 or elongation reduction rolling mills 32 are possibilities as a calibration unit 30.

The production system presented above, as well as a corresponding production method, are particularly suitable as hollow-block casting units 10 in connection with centrifugal casting units 11, 12. By means of centrifugal casting, it is possible to produce multilayer or bimetallic centrifugally cast hollow blocks, which can be hot-rolled on the production system 40 for the production of a seamless hot-rolled tube 70 and by means of corresponding methods. In this way, a tube 70 as shown in FIG. 2 can then be made available as a centrifugally cast tube 71, which has an outer material layer 73 and an inner material layer 74 composed of different materials and having different material properties. Because of the production process and particularly also because of the hot-rolling process in the elongator 20, a mixed layer 75 occurs between the outer material layer 73 and the inner material layer 74. Because of the hot-rolling process in the elongator 20, a hot-rolled centrifugally cast composite material tube 72 is therefore obtained, which has bimetallic properties if the method is managed appropriately.

With regard to concrete method management, it is ensured in the exemplary embodiments that the elongator works at elongations between 2 and 10.

Although only a few embodiments of the present invention have been shown and described, it is to be understood that many changes and modifications may be made thereunto without departing from the spirit and scope of the invention. 

What is claimed is:
 1. A production method for producing a seamless hot-rolled tube comprising: elongating a cast hollow block in a hot-forming elongator with an elongation of 10 or less; including one of the following: (i) circumventing a cross-roll piercing step or interposing a cross-roll piercing step at an elongation below 1.5; (ii) utilizing at least part of the casting heat; or (iii) utilizing at least part of the casting heat and circumventing a cross-roll piercing step or interposing a cross-roll piercing step at an elongation below 1.5.
 2. The production method according to claim 1, wherein the hollow block is heated before elongation in the elongator, tempered in a furnace as a buffer, or heated before elongation in the elongator and tempered in a furnace as a buffer.
 3. The production method according to claim 1, wherein after elongation, the hollow block is calibrated in a calibration unit.
 4. The production method according to claim 1, wherein said cast hollow block is elongated in the hot-forming elongator with an elongation of 8 or less.
 5. The production method according to claim 4, wherein said cast hollow block is elongated in the hot-forming elongator with an elongation of 7 or less.
 6. The production method according to claim 1, wherein the elongator is a longitudinal rolling mill.
 7. The production method according to claim 6, wherein said longitudinal rolling mill is a push bench.
 8. A production system for producing a seamless hot-rolled tube comprising: (a) a hollow-block casting unit; (b) an elongator disposed behind the hollow-block casting unit; and (c) a conveying segment between the hollow-block casting unit and the elongator; wherein said conveying segment is sufficiently short so that part of the casting heat can be utilized for elongation in the elongator; and wherein said conveying segment is interrupted by a furnace, or runs without interruption and has a lock system to and from a furnace, or is interrupted at most by a severing unit.
 9. The production system according to claim 8, wherein the furnace serves as at least one of a buffer, a reheater, and a temperature equalizer.
 10. The production system according to claim 8, wherein the hollow-block casting unit is a centrifugal casting unit.
 11. The production system according to claim 8, wherein the elongator is followed by a calibration unit.
 12. The production system according to claim 11, wherein the calibration unit comprises at least one of a sizing mill and an elongation reduction unit.
 13. The production system according to claim 8, wherein the elongator is a longitudinal rolling mill.
 14. The production system according to claim 13, wherein the longitudinal rolling mill is a push bench.
 15. The production system according to claim 13, wherein the longitudinal rolling mill has an elongation of 2 or more and of 8 or less.
 16. A rolled centrifugally cast tube comprising a hot-rolled centrifugally cast composite material tube.
 17. A seamless hot-rolled centrifugally cast composite material tube produced using a composite material hollow block produced by centrifugal casting. 